I'm building a heavy Octo for aerial photo & video based on the APM2 board + Carbon Core Octocopter1000 with 360 Pano Mount and Mega Radius camera mount.
The power is provided by two Turnigy nano-tech 6000Mah 6C batteries connected to 8 Himodel 40Amp ESCs powering 8 Tiger motor MT3515-15 400Kv motors with Master Airscrew 14x7 3-blade propellers fitted.
The theorical maximum amp draw for each motor is 29Amps making a theorical max Amp draw of 232Amps. I want to measure battery Voltage and current draw but the biggest AttoPilot Current & voltage sensor is rated for 180Amps Max.
I know I'ts impossible or near impossible to go to max Amps with all motors at same time doing AP but given that burning the Attopilot sensor will stop the power feed to the multicopter, and this will result in a more than sure crash, I want to be very conservative and not overload it.
Is there an option to connect two 180Amp sensors to the APM2 board (one on each battery) and get readings?
Two sensors should be capable of handling 360Amps and this would solve my problem.
The simplest way up to 200A unidirectional or bidirectional for you is to use one of the Allegro's ICs ACS75x - http://www.allegromicro.com/Products/Current-Sensor-ICs/Fifty-To-Tw... .
For higher currents, it's better to use current divider technique - http://www.allegromicro.com/Design-Center/Technical-Documents/Hall-... . In this approach, you sense 1/2...1/5....1/10 of the real current for example where the main current flows through the high current schunt part, while the measurement is made in the measurement part ( the schunt has 2 sections ). Then you have to recalculate the real current.
Also for higher currents you can use a current sensing transformer. The problem with them is that they are not as slim as ICs.
If you decide to use another approach - schunt current sensing - high current schunt with a simple and cheap IC as a current monitor, you can use Diodes current monitors - http://diodes.com/products/catalog/list.php?parent-id=79 with a high current schunts from Isabellenhutte for example - http://www.isabellenhuette.de/en/products/ .
There's another approach of using N current monitors with current or voltage outputs and then make a SUM of them with an OpAmp.
If you have any questions, please just ask me.
This way the current will be splitted between both sensors and as a result each sensor will only handle 116Amp at maximum load.
I'd suggest using another approach. At such high currents you should be very very carefull as I'd seen glowing cables!!!
I suggest dividing the current flow to two circuits -> 4 + 4. The current flow do not disturb current reading. Then you can sum the current readings but note that if the full scale of the 180A current sensor is 5V(3.3V), you can't simply sum them. The easiest way is first attenuate each output to 1/2, then sum the two outputs. Thus you'll have 100% full scale at 360A. Also you can first sum them and then attenuate the signal to get within 5V(3.3V) scale. The second approach is much uncomfortable as you need a higher stabilized power supply for the summing OpAmp. Do look at the datasheet of your sensors for the full scale and then decide.
Finally I'm using H07V-K 25mm2 cable between batteries and two power distribution boards.
The power distribution system is arranged this way:
Each 100Amp power distribution board carries one polarity and both are bond with 0,5mm hex spacers, (soldered cables are in opposed sides) this way I have the exact space between outer faces of the boards (up and down) to solder XT60 connectors for the ESCs.
And here came the questions:
Could you specify the circuit needed to atenuate the and then add the signal of the two attopilot sensors? I could install them on the batteries (one on each battery) and since they are installed in parallel should each sensor handle and measure only half the total draw.
I'm also studying the option to use this more secure (but bigger) non invasive Hall Effect sensor Suggestions?
If you don't want to make an additional summing amplifier, have a look here - http://bg.farnell.com/jsp/search/browse.jsp?N=2003+203849+110129494...|0&Ntk=gensearch&Ntt=current+sensor&Ntx=mode+matchallpartial&locale=bg_BG&appliedparametrics=true&getResults=true&suppressRedirect=true&isRedirect=&originalQueryURL=/jsp/search/browse.jsp%3FN%3D2003%2B203849%26Ntk%3Dgensearch%26Ntt%3Dcurrent%2Bsensor%26Ntx%3Dmode%2Bmatchallpartial%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Dbg_BG%26divisionLocale%3Dbg_BG%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D2003%2B203849
You can find here your current sensor.
If you decide to use a summing OpAmp, then have a look here - http://www.ecircuitcenter.com/circuits/opsum/opsum.htm or here - https://www.google.bg/search?hl=bg&lr=&newwindow=1&q=op...
Hi ! Thanks for the links !
I would need to measure about 180-200A, I've got an APM 2.5 with its power module (90A max).
What would I need to do, where do I need to connect the sensor's output ? Would it work like the original power module current sensor?
For example, with one of these current sensors :
Here it is a good high current sensor - http://www.hitecrcd.com/products/aircraft-radios-receivers-and-acce...
You have to follow the APM documentation on where to connect the sensor - http://code.google.com/p/ardupilot-mega/wiki/APM25board
Great sensor ! just what I need ^^ Thank you Nick.
But do you think this sensor is compatible with APM ?
Do I Just need to connect it to port A2 ?
Thank you very much for your help, my problem is almost solved ^^"
Can you confirm if that Hitec sensor works with the AMP2.5?
I would also like to know thanks.
There is a much more straightforward solution: use the 180A attopilot as it measures on a scale of 3.3v and APM measures on a scale of 5.5v, the actual current you can measure is 272Amps!